Facile synthesis of a bismuth nanostructure with enhanced selectivity for electrochemical conversion of CO2 to formate.

Electrochemically converting carbon dioxide (CO2) to formate offers a promising approach for energy conversion and storage. Bismuth is believed to be one of the promising candidates for CO2 electroreduction, but the poor selectivity and complexity of synthesis limit its real application on a large scale. In this work, a facile one-step-reduction method was developed to prepare a bismuth nanostructure in aqueous solution. Owing to its enhanced reactive sites and exposed crystal plane, the prepared Bi nanostructure exhibits excellent performance for CO2 electroreduction, which reaches the maximum faradaic efficiency for formate as high as 92% at a potential of -0.9 V versus a reversible hydrogen electrode. Additionally, the large current density and remarkable durability also reveal its high intrinsic CO2 electroreduction activity. The density functional theory calculation confirms that the formation of intermediate *OCHO that finally converts to formate is thermodynamically favorable on Bi high-index planes. We anticipate that such a facile synthesis strategy and excellent electrocatalytic performance of the Bi nanostructure will be easy to scale up, realizing its industrialization applications in CO2 electrochemical conversion.

Tuning carbon nanotube-grafted core-shell-structured cobalt selenide@carbon hybrids for efficient oxygen evolution reaction.

The electrochemical oxygen evolution reaction (OER) is sparked extensive interest in efficient energy storage and conversion. Cobalt Selenide (CoSe2) is believed to be one of the promising candidates for OER based on Yang Shao-Horn's principle. However, owing to low exposure of active sites and/or low efficiency of electron transfer, the electrocatalytic activity of CoSe2 is far less than expected. In this work, a novel carbon nanotubes (CNT) grafted 3D core-shell structured CoSe2@C-CNT nanohybrid is developed by a general hydrothermal-calcination strategy. Zeolite imidazole frameworks (ZIF) was used as the precursor to synthesis of the materials. It is found that both the calcination temperature and the selenium content can significantly regulate the catalytic performance of the hybrids. The obtained best catalysts requires the overpotential of only 306 mV and 345 mV to reach a current density of 10 mA cm-2 and 50 mA cm-2 in 1.0 MKOH medium, respectively. It also exhibits a small Tafel slope of 46 mV dec-1 and excellent durability, which is superior to most of recently reported CoSe2-based and Co-based materials. These superior performances can be ascribed to synergistic effects of the highly active CoSe2 nanostructure, defect carbon species and the carbon nanotubes exist in the catalyst. Besides, the unique morphology leads to large electrochemical surface area of the catalyst, which is in favor of the exposure of active sites for OER. Due to high efficiency, low cost and excellent durability for OER, the prepared catalysts showed can be potentially used to substitute noble metals utilized in related energy storage and conversion devices.

Synthesis of polyoxometalates derived bifunctional catalyst towards efficient overall water splitting in neutral and alkaline medium.

The development of efficient hydrogen evolution and oxygen evolution reactions bifunctional electrocatalyst for overall water splitting is highly desired but still a great challenge, especially under neutral condition. With the unique properties of polyoxometalate and MOFs materials as well as rich transition metal contents, herein we successfully synthesize a novel bi-phase structure of cobalt and molybdenum carbide coated with nitrogen-doped graphite (Co-Mo2C@NC) which possesses excellent activity as water splitting electrocatalyst at neutral pH. This noble metal-free, bi-phase electrocatalyst exhibits Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) overpotentials of 260 mV and 440 mV at 10 mA cm-2, respectively. The two-electrode system using Co-Mo2C@NC as both the anode and cathode drives 10 mA cm-2 at a cell voltage of 1.83 V with a remarkable long-term stability. Besides, the Co-Mo2C@NC also shows promising activity in alkaline condition that reaches 10 mA cm-2 at a cell voltage of 1.66 V. This work paves a new avenue to the design of the unique, economic and promising non-noble metal electrode materials for practical applications in the electrochemical energy storage and conversion devices.